Friends with benefits, no strings attached, part-time boyfriends, one-night stands, flings, hook-ups, booty calls, last calls. The murky vernacular of campus dating has mystified parents for years, but a new survey might offer some translation.

Researchers from the University of Ottawa have gleaned plenty about the shadowy rules of engagement in casual relationships – no, it's not okay to sleep over after a booty call – after extensive interviews with 18- to 24-year-old students. They also conducted online focus groups with 900 respondents under age 30.

The findings, published in The Canadian Journal of Human Sexuality, delineate four major types of casual sex encounters: the one-night stand, the booty call, the friend with benefits and the "sex" buddy (the actual term is more profane). Each entails very specific rules around initiation, communication, emotional attachment and the inevitable dump, rules that are rarely explicit, yet remain widely understood by teens and twentysomethings.

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The new terminology is a far cry from the dainty monikers used by scientists in the 1960s – "permissiveness without affection" and "premarital coitus."

"Young adults appear to be developing broader conceptualizations of what constitutes a relationship," wrote lead author Jocelyn Wentland, a PhD student in experimental psychology at the University of Ottawa's Human Sexuality Research Laboratory.

"It's about a prolonged adolescence" ahead of increasingly delayed marriages, said Ms. Wentland.

While "casual sex relationship" screams oxymoron to many, those who chronically engage in loose liaisons would beg to differ; it would be worthwhile for all clinicians and sex educators to learn their language, the researchers argue, especially as casual becomes increasingly normal.

The first misconception the researchers clarify is that intercourse isn't always involved in casual sex: Studies have shown that prevalence rates drop to 15 per cent when actual intercourse is involved, shooting up to 75 per cent when "sexual activity" is the descriptor.

Surveys conducted over the past decade suggest friends with benefits (FWB) – pals who develop sexual relationships – are extremely widespread. Some studies estimate that 50 per cent of post-secondary students engage in FWB. While not traditionally monogamous, FWBs are the most "sexually exclusive" of the casual-sex-relationship types: You are expected to disclose information regarding other partners who may be floating around.

"It is the most like a real relationship – it was most likely to lead to a real relationship," said Ms. Wentland. "You respect your friend with benefits."

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Respect aside, secrecy pervades FWB unions, so as not to "ruin group dynamics" – set tongues wagging, that is. While some FWBs evolve into romantic relationships that can eventually be disclosed, others end when one partner finds someone else.

"Sex" buddies are commonly mistaken for FWBs but are actually the reverse, beginning as one-night stands that evolve into something akin to friendship as partners meet more frequently and get properly acquainted. Still, monogamy is not expected and partners go their own way once the appeal has weakened.

One-night stands, meanwhile, are singular sessions typically fuelled by shots at the bar. Booty calls are one-night stands set on repeat.

"These individuals are convenient, transient sexual partners with no emotional investment," the Journal authors write, noting that "emotionally intimate acts" such as hand-holding and even kissing a partner's face were verboten for booty calls, as were sleepovers and breakfasts the next morning. (Sleepovers are acceptable for one-night stands, but not breakfast.)

As for communication styles, the authors found that booty calls rarely call, preferring to text: "A 'booty caller' would sometimes make a telephone call if the caller was too intoxicated to compose a legible text message or if a text message notification would not be loud enough to wake the other individual," the authors explained.

Indeed, with the exception of one-night stands, who don't converse much beyond their drunken collision, and FWBs who talk on the phone, teens having casual sex overwhelmingly communicate via text, with MSN and Facebook chat a close second. This way, "fears of rejection are minimized."

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The death knell for all casual relationships, of course, is emotional attachment, which "violates the idea that this is easy access to sex without the complications, as impossible as that may be for either party," said Ms. Wentland.

Respondents agreed there was no need for a "formal termination conversation" among one-night stands, booty calls or even "sex" buddies – just stop texting. "A booty call could just disappear" and be replaced by some "other bigger and better booty call," according to two women who were interviewed.

This notion of trading up – disposal, even – ran through the focus groups. When isolated from the women, male respondents offered up some unique terms for the one-night stand – "Hit it and Quit it," and "Use 'Em and Lose 'Em" the more genteel among them.

"They're definitely not respectful," Ms. Wentland said of the terms, which she nonetheless wrote off as "male bravado."

While many studies have examined the consequences of casual sex, from risky sexual behaviours to regret, emotional distress and depression, the current study did not. For all the implicit rules, previous research suggests it's women who more often feel the burn when casual arrangements fizzle. Respondents here said women were more likely to get attached during a FWB scenario, while a 2010 Colorado State University study found men were ultimately motivated by sex and women by "emotional connection."

But as Ms. Wentland – and no doubt many a fleeing fling – point out, "There's that implicit, tacit agreement: 'We both knew what this was when we got into it.'"

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So why do so many twentysomethings take casual over committed? "Filling the void/boredom" and "fall-back plan" were two reasons cited, as was the obvious: sexual desire.

"There are women who will say, 'I was only engaging in casual sex with him because I thought he'd be my boyfriend.' But there are lots of other women who say, 'I took him home from the bar because I was horny.'"

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